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Maine outlines targeted releases of parasitoid wasps to help control emerald ash borer
Summary
State entomologists described a biological control program that has released three tiny parasitoid wasp species since 2019; releases require APHIS sign‑off and suitable sites (roughly 40 acres with ~25% ash or connected stands).
Colleen Tierling, an entomologist with the Maine Forest Service, described the state’s biological control program aimed at reducing emerald ash borer (EAB) population pressure over time. "We have 3 tiny little parasitoids. They're wasps," she said, explaining that the agents are highly specific to EAB and were tested extensively before release.
Tierling said the program began releasing approved parasitoids in 2019 after U.S. Animal and Plant Health Inspection Service (APHIS) approvals and that releases are selective: sites must have confirmed EAB presence and be suitable habitat. The state seeks sites of about 40 acres with at least roughly 25% ash, or smaller stands with connectivity, and releases are typically conducted for two summers followed by multi‑year monitoring to detect establishment.
She stressed that biological control is not a silver bullet: parasitoids are unlikely to save large, mature ash trees already standing, but they can reduce EAB population levels and protect future generations of ash. "Biological control EAB is not a silver bullet in any way, shape, or form," she said, adding that the best outcomes are expected where biocontrol is part of an integrated approach including targeted removals and, where appropriate, limited insecticide treatments.
Tierling invited landowners and land managers to volunteer potential sites and said the state can advise on site suitability. She also urged early monitoring (for example, girdle trap trees) so that releases can begin promptly when an infestation is detected locally.
